This invention relates to hydraulically efficient ribbed pipe and particularly to hydraulically efficient ribbed pipe having closed ribs, and the method of making thereof.
Corrugated pipe has been used for many years in culvert and other storm drain type applications. However, corrugated pipe is inefficient because it does not have a smooth inner surface. To achieve more efficient operation and to improve flow, smooth wall pipes, made from concrete or plastic, are used. Plastic pipe is expensive in the larger sizes, has strength problems, and must be properly supported. Concrete pipe is heavy, making installation difficult. Moreover, concrete has problems due to corrosion, depending on the type of liquid being transported.
To overcome these problems, steel pipe is now being manufactured. To achieve proper strength requirements and keep the weight down to reasonable levels, the pipe is typically made from flat sheets that are rolled into a spiral form (typically helical). The spiral pipe is joined by welding or by using a crimp-type lock seam. To increase strength, a rib is typically formed at a point intermediate to the lock seam. Typically, this rib is formed by a die type press. Such construction creates open type ribs. Examples of this type of pipe are found in U.S. Pat. Nos. 4,630,650 to Davis and 4,838,317 to Andre at al. The Davis structure forms either a triangular rib or a "U" shaped rib on one side of the sheet of steel. The opposite side of the sheet is formed with an interlocking fold. As the pipe is rolled into the spiral, the interlocking fold interlocks with a corresponding fold on the rib. Once interlocked, the folds can be crimped to lock the seam. The Andre et al patent teaches a number of open or semi open rib designs. In most cases, these rib designs are formed by rolling the sheet of steel over appropriate dies. Andre et al. teaches the use of semi-closed ribs that can act to secure lining materials to the inner pipe wall surface. Andre et al. teach that ordinary liners have difficulty in adhering to pipe walls. Such linings, as shown in the Andre et al. patent include plastics and concrete liners. Andre et al. also teaches formation of a triangular type rib that is formed by bending the wall upward and outward, forming a "V" shaped channel that is open at the top. A cap is placed over this channel and is crimped into place.
Open rib designs are easy to manufacture. However, an unlined ribbed pipe presents some hydraulic inefficiency. Moreover, the open ribs can become a breeding ground for bacteria. Finally, the size of the ribs in the Andre et al design is relatively small. Attempting to use the ribs as a means to hold a liner is tenuous. The process of forming complex interlocking rib designs is also expensive and time consuming.